In this study, several heat transfer fluids consisting of Poly-Alpha-Olefin (PAO) as base fluid and non-spherical alumina (Al2O3) nanoparticles such as nanorods and nanoplatelets have been used to formulate thermally enhanced nanofluids. Thermal properties such as thermal conductivity and viscosity have been measured, and the corresponding thermal conductivity enhancement has been calculated. The heat transfer coefficient under laminar flow under constant heat flux conditions has been measured experimentally. Results indicate that nanofluids containing spherical and non-spherical nanoparticles depict a Newtonian behavior at low concentrations. Nanofluids containing non-spherical alumina nanoparticles exhibit the greatest thermal conductivity enhancement when compared to pure PAO. Moreover, heat transfer enhancement was also observed when non-spherical nanoparticles were used. Likewise, the percentage enhancement in convective heat transfer coefficient was shown to increase non-linearly with axial distance (x/Di) in a circular heat transfer section. Nanofluids containing non-spherical nanoparticles exhibits a lower Re*Ra (Reynolds number*Rayleigh number) than pure PAO under laminar flow constant heat flux conditions indicating that nanoparticle morphology and composition are the two main factors responsible for convective heat transfer enhancement at low Reynolds number. Convection and axial conduction can explain the increase in Nusselt number when x/Di is greater than 400. The expected radial movement of nanoparticles within the fluid at relatively low Reynolds number could explain the enhanced convection when factoring in changes in viscosity and the effect of buoyancy.

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